No, there's no way to do this with a plugin; RStudio's language system is currently not user extensible. You'll need to make a custom build of RStudio if you want to do this.

A couple of tips:

Building RStudio is not too hard. If you are making a build for Linux, and you have Docker installed, you can build RStudio with your change without installing anything else. See here for more: Building with Docker

We welcome pull requests! If you get it working with your language, you're welcome to submit a PR for consideration.